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American colonists used Indian trails at first, eventually widened them and straightened them as part of a network of quagmire-pocked coach roads connecting major cities along the East Coast. Not until the late 1850s, when Congress appropriated $550,000 for three wagon roads, did anyone going West from the Mississippi River have anything but trackless prairies to drive on. From then on, road networks spread like spider webs across the U.S. In 1904 the U.S. Office of Road Inquiry took a national highway census that showed 2,000,000 miles of roads, just 250 miles of them paved.

These were the times that Professor Harmer Davis, transportation expert at the University of California, calls the period of caveat viator—let the traveler beware. With the '20s came the concept of traffic engineering, which finally adapted the carriage road of history to the internal-combustion car, providing gradual curves, smooth surfaces, low grades, road markers—and some helpful innovations. One was the parkway, which was born along the Bronx River in New York's Westchester County in 1922 and pioneered the principle of separated opposing lanes. Another was the cloverleaf, the essential invention that lets traffic on two divided highways cross and merge in all possible directional combinations without interrupting flow; the first was built at Woodbridge, N.J., in 1928.

The third phase of U.S. road history is the present period of making the road fit the environment. Land use, the natural setting, social conditions and human psychology are its concerns. It acknowledges that the private car is and for scores of years will be the most used form of transportation. Its expression is the U.S. Interstate Highway system, and its symbol is the red, white and blue shield that seems to say, "Heave a sigh of relief and get moving."

Gentle Grades & Artful Curves

These great Roman roads of today combine half a dozen principles to achieve a qualitative advance over any earlier road system, or any foreign system. The freeway's wide median strip virtually abolishes head-on collisions and headlight glare. Passing is made so easy that one four-lane freeway can carry about ten times as many cars as two two-way roads. Freeway cloverleafs eliminate the need for intersection stopping; limited access banishes blind entrances and overly frequent inflows of traffic. Gentle grades, ample widths and curves of an easy mathematical beauty let drivers see at least twice as far ahead as the distance they might need—even at the engineered 70 m.p.h.—to come to a stop. The same curves, plus the swirling cloverleafs, give much of the system a pre-Raphaelite art and grace.

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